Post-tension concrete construction dominates Florida's multi-story residential and commercial building stock. If you work on buildings in Miami, Fort Lauderdale, Naples, Sarasota, or virtually any coastal Florida market — you are working with PT slabs regularly, whether you know it or not.

This guide explains what post-tension cables are, what happens when one is severed, how GPR detects them, and what scanning procedure gives you the highest confidence before any core drilling or concrete cutting operation.

What Are Post-Tension Cables?

Post-tension construction uses high-strength steel tendons encased in plastic sheaths, threaded through concrete slabs and tensioned against anchors at the slab edges after the concrete cures. This places the concrete in compression, allowing thinner slabs to span greater distances and carry heavier loads than conventional rebar-reinforced construction.

Unbonded PT tendons — the most common type in Florida — consist of a single 0.5-inch or 0.6-inch diameter seven-wire strand coated in grease and encased in a plastic sheath. The tendon is tensioned to approximately 33,000 pounds of force after the concrete reaches design strength.

⚠️ Critical Safety Fact: Severing a post-tension tendon releases 33,000 pounds of stored energy instantaneously. The cable end can travel several feet through or along the slab, puncture forming materials, and injure workers. In extreme cases, cutting multiple tendons in a concentrated area can trigger progressive slab failure.

How Prevalent Are PT Slabs in Florida?

Post-tension construction has been the dominant method for multi-story construction in Florida since the late 1970s. The reason is practical: Florida's flat terrain, high water table, and long building spans make PT construction economical. As a result:

  • The majority of residential high-rises built after 1980 in South Florida use PT slab construction
  • Most commercial parking structures in Florida are post-tensioned
  • Many commercial office and retail buildings in the 1990s–present use PT elevated slabs
  • Even some single-family luxury homes use PT slabs in South Florida

If you are not scanning for PT cables before every core drilling or saw cutting operation in Florida, you are gambling. The scan cost is a fraction of the liability exposure from a severed tendon.

How GPR Detects Post-Tension Cables

Ground penetrating radar detects PT cables based on the electromagnetic contrast between the steel tendon (and its plastic sheath) and the surrounding concrete matrix. The signal returns a hyperbolic reflection signature — the same shape as rebar — but with characteristics that distinguish it from conventional reinforcing steel.

GPR Signature Differences: PT Cables vs. Rebar

Rebar Signatures

  • Uniform depth across the slab
  • Regular grid spacing (typically 12" or 18" on center)
  • Consistent hyperbolic amplitude
  • Typically round cross-section

PT Cable Signatures

  • Varying depth — tendons drape between supports
  • Narrower diameter (0.5"–0.6") than typical rebar
  • Often runs parallel to one direction only
  • Undulating depth profile when scanned longitudinally

The varying depth profile is the most reliable distinguishing feature. Unlike rebar, which maintains consistent depth, PT cables are lowest at midspan (where concrete tension is greatest) and highest at supports. A skilled GPR operator can use this signature to confidently identify PT tendons in most scan conditions.

Which GPR Equipment Works Best for PT Cable Detection?

GSSI NC 3D Concrete Scanner — Best for PT Mapping

The GSSI NC 3D Scanner ($550/day) is the highest-confidence tool for PT cable detection. It simultaneously collects data in multiple scan lanes and processes it into a C-scan (plan view) of the entire slab — showing both rebar and PT tendons in a single overhead image. For high-risk PT scanning in luxury buildings, parking decks, or complex renovation projects, the NC 3D is the professional standard.

GSSI StructureScan Mini XT — Best Value for Standard PT Scanning

The GSSI StructureScan Mini XT ($350/day) with its 2700 MHz antenna provides the resolution needed to distinguish PT cables from rebar in most Florida building conditions. It's the most-rented scanner for PT work on typical renovation projects. The built-in 3D processing software generates a plan view from manual grid scanning.

GSSI 2300 MHz Palm XT — For Walls and Tight Spaces

The GSSI Palm XT ($390/day) is the right tool when PT tendon detection is needed in concrete walls, columns, or locations where the Mini XT's larger footprint can't fit. The Palm XT also excels for very shallow PT detection in thin slabs.

Important: GPR cannot always reliably distinguish PT cables from rebar in slabs with very dense reinforcing steel or extreme concrete saturation. When scan confidence is uncertain, consult a structural engineer or hire a concrete scanning service for interpretation support.

PT Cable Detection Protocol for Florida Projects

  1. Identify the slab type. Review as-built drawings if available. Look for anchor pockets at slab edges — cast-in pockets with PT tendon end caps are a positive indicator of PT construction.
  2. Select the correct scanner. Use 2700 MHz or higher frequency for standard PT slabs. For thick slabs or deep PT tendons, the Flex 25 antenna provides better depth penetration.
  3. Scan in both directions. PT tendons typically run in one direction, but scanning in both X and Y reveals the full picture. Grid scanning allows 3D processing for a plan-view map.
  4. Mark tendon locations on the slab surface. Use paint marking to transfer scan data to the concrete. Mark PT tendons distinctly from rebar (different color).
  5. Select drill locations with 2"+ clearance from any PT cable. Never drill within 1.5" of a detected PT tendon.
  6. Document the scan before work begins. Photograph the marked scan area for project records.

Florida Renovation: High-Risk PT Scenarios

Certain renovation tasks in Florida are especially high-risk for PT encounters:

  • Bathroom drain relocations in condominium renovation — cutting through a PT slab for a new drain is one of the most common PT failure events in Florida
  • HVAC/MEP penetrations through elevated parking decks — almost all Florida parking decks are post-tensioned
  • Anchor bolt installation in PT slabs for structural attachments, overhead supports, or equipment mounting
  • Stairwell modifications in multi-story PT buildings

In each of these scenarios, a GPR scan before drilling is the single most important safety step. The cost of scanning is always less than the cost of a PT failure.

Renting vs. Hiring for PT Cable Detection

If your crew will be performing regular concrete scanning, renting GPR equipment and training your operators is the most cost-effective approach long-term. Our Concrete Scanning Training course includes hands-on PT cable scanning with professional equipment.

For one-time projects, complex buildings, or legal/structural documentation purposes, hiring a professional concrete scanning service may be more appropriate. Read our comparison: GPR Rental vs. Hiring a Scanning Service.

Need PT Cable Scanning Equipment in Florida?

We deliver professional GPR systems for PT cable detection same-day anywhere in Florida. Call to confirm availability and get the right scanner for your slab type.